/Engine/Source/Runtime/Engine/Classes/Materials/MaterialExpressionStrata.h
class UMaterialExpressionStrataVerticalLayering : public [UMaterialExpressionStrataBSDF](API\Runtime\Engine\Materials\UMaterialExpressionStrataBSDF)
FExpressionInpu...
Base
Substrate material layer below the Top material layer
uint32:  1
bUseParameterBlending
Merge Top and Base into a single material by mixing their inputs rather than their evaluation.
FExpressionInpu...
Thickness
Thickness of the Top material layer
FExpressionInpu...
Top
Substrate material layer on top of the Base material layer